The France international was highly critical of his side's performance in north London, claiming they failed dismally to cope with opponents he feels they could have matched
The France international turned in an impressive individual performance in London, saving Mesut Ozil's first-half penalty as well as making a string of other fine stops.
However, he was powerless to prevent the Gunners from coasting to a 2-0 win courtesy of a Jack Wilshere double, which consigned the visitors to a fifth successive defeat in this year's competition.
"If I told you we are at the same level as Arsenal, I would be lying," Mandanda told reporters after the game.
"Our opponents are far above us. I really think we should be on a par with such an opponent - we were far from this tonight.
"Our team struggled against the constant stream of Arsenal attacks."
Marseille will complete what has been a dismal European campaign with a home game against Borussia Dortmund next month.